This invention relates to a novel, efficient process for parboiling rice.
The parboiling of rice has its genesis principally in India. In the early history of parboiling, the rough (paddy) rice was simply soaked in warm water overnight and then dried in the sun. The apparent benefit from parboiling was that the rice hulls were split open and were thus easily removed from the rice kernel. In modern times, it has been further realized that such parboiling provides a more nutritional rice as thiamine and other essential nutrients, which are normally present in the rice bran, migrate to the rice endosperm during the water soaking. Since almost all rice is milled to remove the bran, this migration preserves at least some of the nutritional values originally contained in the bran. Parboiling is also beneficial as the starch in the rice endosperm is changed from a crystalline amorphic state to an amorphous state. With the starch in the crystalline state, the kernel is tougher and thereby provides a higher yield of whole rice kernels after milling.
Today, approximately 22% of the rice produced in the United States is parboiled commercially. Commercial parboiling processes generally include the steps of: (1) soaking the rough rice in 50.degree.-70.degree. C. water for 3 to 4 hours to yield a rough rice having a 30 wt. % water content; (2) draining the free water from the soaked rough rice; (3) applying steam heat under pressure for 15 to 20 minutes to the soaked rough rice to effect gelatinization of the rice starch and to raise the water content to about 35 wt. %; and (4) drying the steamed rice with hot air to reduce its water content to about 14 wt. % water. (All of the above weight percents are on a wet basis.) The dried, parboiled rough rice is then ready for milling.
Even though this type of process is widely used, it is disadvantaged in that the use of 50.degree.-70.degree. C. soaking water, steam under pressure and hot air make it energy intensive, time consuming and thus, depending upon the source of fuel, expensive. It has been calculated, based upon natural gas having a heat content of 33.5 MJ/m.sup.3 and a cost of $0.21/m.sup.3, that the energy requirements for the soaking, steaming and drying would cost at least $16.14/1000 Kg of parboiled rough rice. Such an expense makes it difficult for processors having no cheaper fuel available to them to compete in the world market.
It is therefore an object of this invention to provide a process for producing parboiled rice which is energy efficient, exhibits high yields and reduces process times.